The invention relates to a method of detecting the positional accuracy of register and folding or cutting edges on flat copies in folders which are arranged downline from rotary printing machines for single-side or multi-side printing of material webs.
U.S. Pat. No. 5,568,767 is concerned with a method and a device for maintaining the register and the cut-off register in rotary printing machines. In a first method step, the position of each printed image on the material web is registered. This is followed by the generation of a reference signal which corresponds to a desired or nominal position of the image on a material web. A data stream corresponding to the register deviations is then generated, control commands to the control unit of the rotary printing machine being transmitted continuously and being based upon the data stream representing the register deviations. In addition, a control data stream which influences the speed of the rotating system is generated, the control data stream being determined by using the calculated changes in a data stream corresponding to the register deviations. Finally, the data streams which influence the machine torque are generated, these machine torque-influencing data streams being determined from the changes of a data stream which influences the speed of the rotating system.
By deviations determined in this manner, the phase angle of the cutting cylinder is influenced in order to produce the maintenance of register between the position of the printed image and the position of the cut edge.
The published International Patent Document WO 97/36749 is concerned with a method for the qualitative assessment of processed material. In this proposed method, by at least one photoelectric sensor and an evaluation device cooperating with the latter, image regions on the inspected material and assigned to possible fault sources are registered. In each case, the fault sources are represented by the printing plates of the printing-plate cylinder. Respective counting pulses are registered in separate counting units for copies which are found to be good and for printed copies which are found to be poor.
In view of the indicated prior art, it is accordingly an object of the invention to provide a method of the foregoing general type which is reliable and operates quickly for detecting the position of folding or cutting edges on flat copies and for detecting the position of the printed image.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of detecting the positional accuracy of register and one of folding and cutting-edge positions, respectively, on flat copies, including scanning a prescribable recording field on the copy by a detector, which comprises determining the position of the printed image and of the folding and cutting edges, respectively, by contrast transitions extending through screen fields.
In accordance with another mode, the method invention includes prescribing scanning zones in the recording field by a user of the method.
In accordance with a further mode, the method invention includes superimposing screens on defined scanning zones in the recording field.
In accordance with an added mode, the method invention includes providing sets of vertical lines for covering at least one of the folding and the cutting edges, respectively, in the screen fields.
In accordance with an additional mode, the method invention comprises providing the screen fields with horizontal lines and vertical lines sweeping over edge regions.
In accordance with yet another mode, the method invention includes placing markings at the vertical lines interrupted at a transition between background and copy.
In accordance with yet a further mode, the method invention includes determining the course of the folding spine from the position of the markings.
In accordance with yet an added mode, the method invention includes determining the course of the cutting edges from the position of the markings.
In accordance with yet an additional mode, the method invention includes determining the position of the printed image from the markings of the screen field, which distinguish contrast leaps.
In accordance with a concomitant mode, the method invention includes determining the distance between the printed image and a respective folding and cutting edge from the course of the sequence of markings of the screen field, respectively, representing one of a folding spine and the cutting edges, respectively, and the markings of the screen field representing the edge of the printed image.
The objective of the invention is thus achieved by providing, in a method of detecting the positional accuracy of register and cutting or folding edges on flat copies, that a prescribed or predefined recording field on the copy be scanned by a detector, and that the position of the printed image and the position of folding or cutting edges be determined by using contrast transitions running through screen fields.
The advantages associated with the method proposed according to the invention reside in the fact that contrast leaps in screen fields are detectable in real time, and no evaluation routines which consume evaluation time have to be executed. With the selected procedure based upon the detection of contrast steps, the position of folding or cutting edges on flat products can be determined accurately, with an accuracy of xc2x10.1 mm, so that a self-diagnosis system which responds rapidly and extremely reliably in a folder arranged downline from a rotary printing machine can be made available.
In a further development of the concept upon which the invention is based, provision is made, within the recording field of a detector which can be constructed as a CCD camera, for example, to define various scanning zones and to configure them so that they can be defined by the user, the scanning zones, respectively, being of particular interest to the user. The scanning zones are, for example, the folding spine, a folded edge or even the edge region of a printed-image. These regions of interest to the user have screen fields, respectively, superimposed thereon. Depending upon the scanning zone of interest, respectively, the screen field can be formed differently. For example, those screen fields with which the position of the folding spine or the position of a cutting edge are detected contain a pattern of lines extending substantially perpendicularly to the respective folding or cutting edge. Screen fields with which the position of the printed image may be detected contain a pattern of lines which extend in the vertical and in the horizontal direction, respectively.
The screen fields or patches with the differently configured line patterns thereof are preferably placed in those zones wherein sharp contrast leaps occur, which can be evaluated. The contrast leaps located in the screen fields or patches are preferably interpreted as an interruption to the pattern of lines extending vertically or both vertically and horizontally and, if added up appropriately, reproduce the courses of folding or cutting edges or of the edge region of interest of printed images. By the rectilinear courses which result from the markings, the distance between the folding or cutting edge of the copy relative to the printed image may be determined, a distance which is critical for determining the correct register position of the printing plate on the printing-unit cylinders of the rotating system connected upline from the folder.
The user of the method proposed by the invention is able to define, by preselecting scanning zones which are of specific interest to him, individual regions which are of interest to him and which can vary to an extreme extent from printing subject to printing subject, as well as from print job to print job.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of detecting the positional accuracy of register and folding or cutting edges on flat copies, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.